The driving forces in the transceiver manufacturing industry are reducing the form factor sizes, increasing the data transfer rates, and decreasing the costs. To achieve all of these goals, the conventional butterfly-type or transistor outline (TO) can design approach must be replaced with a more exotic component packaging approach. However, to provide an OSA that can be used over a wide range of data transfer rates and products, the OSA must use controlled impedance connections for the high speed RF electrical signal path between the OSA chip and the transceiver electronics. Moreover, the total number of component parts must be reduced, and manufacturable from readily available materials. The assembly processes, including optical alignment, must be simplified and/or automated to reduce labor costs and increase production rates, and the fiber receptacle components should support a variety of wavelengths.
Conventional OSA designs, such as the one disclosed in U.S. Pat. No. 5,537,504, issued Jul. 16, 1996 to Cina et al and assigned to the present Applicant, include a opto-electronic (O/E) transducer 4 mounted in a container 25, which is sealed by a window 26. Solid metallic leads 23 and 24 extend through the rear of the container 25 for soldering to other electrical leads or directly to a transceiver PCB. The Cina et al device will suffer from poor signal integrity at high data transfer rates, because the RF signals need to transmit through the leads 23 and 24, which limits the quality of the transmission and the positioning of the transceiver PCB. The use of flexible-tape conductive wiring has been disclosed in U.S. Pat. No. 5,005,939 issued Apr. 9, 1991 to Arvanitakis et al and assigned to the present Applicant, but only for connecting the existing leads of an OSA to the transceiver PCB. Moreover, the Arvanitakis et al device does not disclose the use of controlled signal impedance conductors required for high-quality high-data rate signals.
Conventional OSAs which are aligned with the optical axis of the optical coupler, generate unwanted back reflections. Solutions for eliminating back reflections in receiver optical sub-assemblies include mounting the photo-detector at an angle and/or providing an index matching block at the fiber/lens interface, as disclosed in copending U.S. patent application Ser. No. 60/539,219 filed Jan. 26, 2004, which is incorporated herein by reference. Alternatively, as disclosed in copending U.S. patent application Ser. No. 60/541,076 filed Feb. 2, 2004, which is incorporated herein by reference, the lens axis can be offset from the main optical axis to impart a tilt to the beam of light. Unfortunately, none of these solutions are suitable for TOSA designs, particularly TOSA applications with back facet monitor photodiodes.
An object of the present invention is to overcome the shortcomings of the prior art by providing an optical sub-assembly with a controlled signal impedance between the transducer chip and the transceiver PCB.
Another object of the present invention is to maximize functionality, while minimizing the size of the transducer chip to conform to small form factor design restrictions.